Storage control unit and method for handling data storage system using thereof

ABSTRACT

For providing a storage control unit to be connected to a fiber channel, in which a new storage control unit is added onto the fiber channel network during on-line operation and succeeds control information of a logical unit from the storage control unit which has been existing before, so as to be in charge of a process request issued to that logical unit from a host computer thereafter, wherein a control memory being able to memorize the control information is provided in each of the storage control units  30  and  40 , which information is necessary when succeeding or taking over the logical unit and is represented by such as construction information of a magnetic disk drive within a disk drive unit  20  and construction information of the logical unit, so on. The contents of the control memory within the storage control unit  30  is copied into the control memory of the storage control unit  40  when the new storage control unit  40  is added onto the fiber channel network.

BACKGROUND OF THE INVENTION

The present invention relates to a storage control unit for controllingstorage devices, such as magnetic disk devices, magnetic tape devices,optical disk devices, opt-magnetic disk devices, library devices and soon, so as to manage input/output (accesses) thereof to a host apparatusor device(s) of higher level, and in particular to a controller and adata storage system using thereof, in which fiber channels are used asroutes or channels for accessing to such the storage devices.

In more detail, the present invention relates to a computer system, inwhich fiber channels standardized by ANSI X3T11 are applied asinterfaces among the host computer(s), the storage devices such as themagnetic disk devices, and the storage control unit(s), and relates to adata storage system, in which a new storage control unit(s) is added toduring an online operation of the computer system, thereby enabling todisperse or decentralize loads between or among the storage controlunits or to centralize functions which are conducted by pluralcontrollers.

Conventionally, relating to install of an additional storage controlunit(s), for example in Japanese Patent Laying-Open No. Hei 7-20994(1995), there is described an enlargement in scale, especially, in amemory system of a large-scaled computer, by means of additionalinstallations of a connecting adopter to the host computer in the memorysystem, a connecting adopter to the disk drive device and a shared cachememory, as well as function of inserting and extracting of live wires.And, there is proposed a manner wherein, the connecting adopter to thehost computer, the connecting adopter to the disk drive unit and theshared cache memory mentioned above are installed one by one on aninterior bus in the memory system.

The technology disclosed in Japanese Patent Laying-Open No. Hei 7-20994(1995) adopts a shared cache memory method which is used generally inthe memory system of the large-scaled computer, wherein each of theadopters connecting to the host computer(s) reads control information ina logical unit(s) located in the shared cache memory on the interiorbus, sequentially, therefore it is able to access to a random logicalunit without necessity of process of succession (i.e., taking over) ortransfer of the control information of the logical unit between theconnecting adopters to the host computer(s).

Also, relating multiplexing of the storage control units, each havingthe cache memory, for example in Japanese Patent Laying-Open No. Hei7-160432 (1995), there is described a method, wherein the storagecontrol unit is duplicated, while one of the storage control units is ina waiting condition as a standby storage control unit when occurringtrouble in the other, thereby achieving redundancy of the storagecontrol unit. Further, in Japanese Patent Laying-Open No. Hei 8-335144(1996), there are also described the decentralization of loads byduplication of the storage control units and the redundancy of thereofwhen occurring problem therein.

SUMMARY OF THE INVENTION

In the technology in the above-mentioned Japanese Patent Laying-Open No.Hei 7-20994 (1995), however the control information of the logical unitis stored on the shared cache memory on the interior bus, therefore theenlargement of scale can be carried out only within a case or housing ofone memory system.

In the technology in the above-mentioned Japanese Patent Laying-Open No.Hei 7-160432 (1995) or Hei 8-335144 (1996), however there is necessitythat, in the storage control unit to be duplicated, each storage controlunit must be connected physically in advance when being in a conditionof off-line, and setting must be done on the logical unit which the eachstorage control unit takes in charge of, when operating under normalcondition and when problem occurs therein. Further, the controlinformation of the logical units are transferred by using the interiorbus, therefore it depends on initial setting, and does not haveexpandability during the on-line operation.

For achieving expansion of functions with flexibility, it is enough thatas the bus or route on which a new storage control unit is added isadopted an interface which is used for connecting with the hostcomputer(s), that each storage control unit to be added further has it'sown cache memory, and that the control information of the logical unit(one logical drive or a group of plurality of logical drives) is copiedinto the above-mentioned cache memory as a logical unit of the storegedevices.

According to the present invention, there is established a data storagesystem, in which a fiber channel standardized by ANSI X3T11 is appliedto, for the host device(s), the storege device(s) such as the magneticdisk device and so on, and the storage control unit(s).

And, in said system, a new storage control unit is added onto the fiberchannel network during on-line operation, so as to succeed or take overthe control information from the existing storage control unit, therebyachieving load distribution between the storage control unit being newlyadded and the existing storage control unit.

The new storage control unit has a means of a function for obtaining(i.e., succeeding) the control information by a unit of the logical unitfrom the existing storage control unit on the fiber channel networkthrough the fiber channel network, when being added to the existingfiber channel network during the on-line operation of the computersystem. Upon completion of the obtaining or succeeding of the controlinformation, it serves under the storage control unit, into which apredetermined logical unit is added.

The storage control unit being newly added to processes a commandprocess request if it is issued from the host computer, for the logicalunit which serves under the control of it. In this manner, the storagecontrol unit being newly added to and the existing storage control unitshare or distribute the load between them.

The load distribution according to the present invention can be appliedeven if a plurality of the existing storage control units on the fiberchannel network have no means nor function of performing the loaddistribution and integration during the on-line operation. However, whenputting the present invention into the embodiment, there is necessity toestablish a function for conducting the succession of the controlinformation.

Further, when succeeding or taking over the control information by theunit of logical unit, an operator establishes a means or a function ofdesignating start for the succession of logical unit and the operationmode thereof during the operation of succession on the host computer orthe storage control unit, by using management tool being operative onthe host computer which is connected to a network, such as the fiberchannel network, the LAN (Local Area Network) and so on, or by using apanel of the storage control unit, thereby enabling to perform theaddition of the new storage control unit at an appropriate timing.

Further, in more details, the storage control unit which is newlyconnected to the fiber channel network has the means or function ofsucceeding the information for the purpose of identifying the storagecontrol unit uniquely from the host computer, i.e., N_Port address, fromthe existing storage control unit which is connected to the fiberchannel network and owns the logical unit to be succeeded, whenperforming the succession of the control information by the unit of thelogical unit. Thereby, it is not necessary to change or alter the routeof the command process request which is issued from the host computer.

The storage control unit according to the present invention has acontrol memory, and it has the means or function of memorizing thecontrol information on said control memory, which is necessary for thesuccession of the logical unit and can be represented by, such as aphysical drive control table, into which are stored the kinds of themagnetic disk device or the others, the memory capacities of the storagedevices, the number of blocks, the condition of each storage device, theconstructive information of RAID (Redundant Arrays of InexpensiveDisks), etc., and a logical unit control table, into which are storedheader LBA (Logical Block Address) and last LBA of the logical unit.

And, the storage control unit which is newly added onto the same fiberchannel network has a means or function of copying the above-mentionedcontrol information, from the control memory on the storage control unitwhich has already been existing before on the above-mentioned fiberchannel network to the control memory of the storage control unit whichis newly added.

The above-mentioned control memory on the storage control unit may be ofa volatile one, however is of a non-volatile memory, in general. Also,by writing the contents (i.e., established information on the controltable or the others) into the storage device, such as the magnetic diskdevice or the others which is connected to the fiber channel network, itis possible to obtain the same effect as obtained when the controlmemory is made of the non-volatile memory. Namely, when occurring abruptinterruption in the electric power source, the storage control unit canmaintain the established information permanently, until when performingthe reset of that established information, for example.

Also, by using the succession of the control information by the unit oflogical unit during the on-line operation, according to the presentinvention, it is also possible to integrate or gather several processeswhich are conducted by the plural storage control units into anarbitrary storage control unit.

In a method for adding a new storage control unit, (1) after connectingthe new storage control unit to the fiber channel network physically,(2) a link set is issued from that storage control unit side to thefiber channel network, so as to perform logical log-in into the fiberchannel network. (3) Thereafter, the operator conducts acknowledgment ofthe storage control unit(s) from the management tool on the hostcomputer which is connected to the fiber channel network, or from apanel of the storage control unit, (4) setting or establishing adesignation of the logical unit of which the storage control unit beingnewly added is in charge, an instruction of start of the succession oflogical unit, and a manner of response when the process request isissued from the host computer to the storage control unit which hasalready been existing on the fiber channel network before, during thesuccession of that logical unit, and (5) the transfer of the controlinformation of logical unit from the storage control unit which hasalready been existing on the fiber channel network before to the storagecontrol unit which is newly added. (6) Further, in the storage controlunit which has already been existing on that fiber channel networkbefore, a plurality of the N_Port addresses, i.e., the information foridentifying the storage control units uniquely from the host computer,are established, (7) and the storage control unit which is newly addedto the fiber channel network succeeds or takes over a portion of theabove-mentioned N_Port addresses, thereby rendering the change or alterof the route for the command process request unnecessary. (8) Further,the storage control unit, existing on the fiber channel network duringthe on-time operation of the computer system, succeeds or takes over thecontrol information by a unit of the logical unit from the other storagecontrol unit which is connected to the same fiber channel network, (9)so as to be in charge of the command process request being issued fromthe host device to that succeeding logical unit thereafter, (10) therebyachieving the load distribution between or among the storage controlunits existing on the fiber channel network. (11) Depending uponnecessity, the integration of processes which are performed by theplurality of storage control units into an arbitrary storage controlunit is performed by applying the technology of succeeding the controlinformation of the logical unit during the on-line operation therein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of the hardware structure for showing an embodimentaccording to the present invention;

FIG. 2 is a view of internal hardware structure of a disk control unitaccording to the embodiment;

FIG. 3 is a view of the hardware structure where Fabric topology isapplied into a fiber channel network;

FIG. 4 is a view of the hardware structure where a plurality of FC-ALloops are applied into the fiber channel network;

FIG. 5 is a view for showing a format of a frame as a basic unit, withwhich data is transferred on the fiber channels in the presentembodiment;

FIG. 6 is a view for showing a format of a frame header which constructsthe frame shown in FIG. 5;

FIGS. 7(a) and (b) are views for showing a format of a pay load ofFCP_CMND as a constructive element of the frame shown in FIG. 5, and aformat of FCP_CDB constituting that pay load, respectively;

FIG. 8 is a view for showing a format of the pay load of FCP_RSP as theconstructive element of the frame shown in FIG. 5;

FIG. 9 is a view for showing sequences of an Inquiry command;

FIG. 10 is a view for showing sequences of a Mode Sense command;

FIG. 11 is a view for showing sequences of a Mode Select command;

FIG. 12 is a view for showing a format of a physical disk drive controltable which is stored in a control memory within the disk control unitin the present embodiment;

FIG. 13 is a view for showing a format of a logical unit control tablewhich is stored in the control memory within the disk control unit inthe present embodiment;

FIG. 14 is a flow chart for showing operation sequences of the diskcontrol unit which is newly added to the fiber channel network in thepresent embodiment;

FIG. 15 is a flow chart for showing the operation sequences of amanagement tool which is installed in a host computer in the presentembodiment;

FIG. 16 is a view for showing a format of a management tooladministration table, into which is stored administration information ofthe management tool installed in the host computer in the presentembodiment; and

FIG. 17 is a constructive view of a data storage system achievingunnecessary of change in access route from the host computer, aftercompleting succession of the logical unit between the disk controlunits, in the present embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Hereinafter, embodiments according to the present invention will befully explained by referring to the attached drawings. Here will begiven explanation only on an embodiment in which a magnetic disk device(hereinafter, described by a disk drive unit) is applied, however intoit also an optical disk device and a tape memory device, etc., can beapplied, in place thereof. And, since the disk drive unit is used in thepresent embodiment, therefore the storage control unit comes to be thedisk control unit hereinafter.

FIG. 1 shows the hardware structure of an embodiment according to thepresent invention, in particular, in a case where a connection mode(topology) of FC-AL (Fiber Channel Arbitrated Loop) is applied into afiber channel network.

In FIG. 1, a reference numeral 10 is a host computer having a centralprocessing unit (CPU) for data processing. A reference numeral 60 is afiber channel network, being connected to various devices through FC-ALhubs and operating according to the FC-AL topology.

A reference numeral 20 is a disk drive unit, into which data from thehost computer A (10) are stored, and it is constructed with a pluralityof magnetic disk drives. By dividing the plurality of the disk drivedevices constituting the disk drive unit 20 logically and defining thedivisions into areas arbitrary RAID levels, redundancy can be achievedwhen trouble occurs in the disk drive unit, thereby enabling to protectfrom loosing of data when the trouble occurs in the disk drive unit.This division is called by RAID group. An area of an access unit of SCSI(Small Computer System Interface) which is further divided logicallyfrom the RAID group, is called by a logical unit. This area has a numbercalled by LUN (Logical Unit Number).

In the present embodiment, the disk drive unit 20 has a logical unit 0(21) and a logical unit 1 (22), however the number of the logical unitsmust not to be only two (2) as shown in FIG. 1 (i.e., with the fiberchannels in conformity with the SCSI-3 standard, at the most 64 logicalunits can be divided for each fiber channel ID. Also, in FIG. 1 is shownthe example of the case where the number of the disk drive unit is one(1), however it does not matter even if the disk drive unit may beprovided on the fiber channel network in plural thereof. In a datastorage system of large capacity being constructed with the plurality ofdisk drive units, a disk control unit very often falls into a conditionof shortage in processing capacity thereof, and the present invention isvery effective when the disk control unit of the computer system fallsin such the shortage in the processing capacity thereof.

Also, in the view of the internal structure of the disk control units 30and 40 shown in FIG. 2, a reference numeral 31 is a fiber channelcontroller which controls data transfer on the fiber channel network andfurther analyzes commands sent from the host computer 10, so as toperform DMA (Direct Memory Access) transfer of the data to a cachecontroller 34. A reference numeral 32 is a non-volatile control memoryfor storing control information which is necessary when succeeding ortaking over micro-programs and the logical units for controlling theoperation of the disk control unit(s). A reference numeral 33 is acentral processing unit (CPU) for controlling the disk controllers as awhole. A reference numeral 34 is a cache control unit for controllingread and write (i.e., input and output) of data into a cache memory, anda reference numeral 35 is a cache memory into which data to be writteninto and read out from the disk drive unit 20 is stored contemporarily.A reference numeral 36 is a panel for changing or referring operationsettings of the disk control unit(s).

A reference numeral 50 is a host computer having a management tool forcontrolling the operations of the disk control units 30 and 40. In thepresent embodiment, the host computer B (50) has the management tool,but it does not matter that the host computer A (10) may have themanagement tool. Further, the interface between the host computer B (50)installing the management tool and the disk control unit 30 or 40 may bea network system, such as a LAN, through which remote control can beachieved.

Next, explanation will be given on flow of control and flow of data in acase where the host computer A (10) performs data transfer through thedisk control unit 30 with the disk drive unit 20, by taking as oneexample.

When the host computer A (10) sends an access request, the fiber channelcontroller 31, which acknowledges this request, issues an interruptionrequest to the CPU 33. The CPU 33 analyzes a command from the hostdevice A (10), and then reads out information from a physical disk drivecontrol table, which stores the memory capacities and the number ofblocks of the magnetic disk drives within the control memory 32,condition of each of the magnetic disk drives and information of theRAID structure, and information from a logical unit control table whichstores top LBA (Logical Block Address) and last LBA therein.

In a case where the access request from the host computer A (10) is awrite command, the CPU 33 issues an instruction of data transfer to thefiber channel controller 31, and then the write data transferred fromthe host computer A (10) is stored into the cache memory 35 through thecache controller 34, while the fiber channel controller 31 makes areport of completion in writing to the host computer A (10). Afterreporting of the completion in writing, the CPU 33 controls the fiberchannel controller 31 so as to write the above-mentioned write data andredundant data into the logical units 21 and 22 of the disk drive unitthrough the fiber channel network.

In this instance, if the RAID level of the logical units storing thewrite data is RAID 5, upon the disk control unit 30 and the disk driveunit 20 are needed processes of very high load, such as, processing ofreading out of old data and old redundancy data for executing thestoring of write data, processing of generating new redundancy data, andprocessing of storing of the above-mentioned write data and the newredundancy data. This is called by a Write penalty process.

In this Write penalty process, though the fact that a large number ofaccesses to the disk drive unit 20 are generated can be one of areasons, further than that, due to the fact that much amount of time isneeded for execution of the micro-program of the disk control unit 30,which controls the disk drive unit 20, therefore the CPU 33 of the diskcontrol unit 30 often falls into a condition of shortage of capacity inprocessing thereof. According to the resent invention, with provision ofan additional disk control unit 40 during the on-line operation, therecan be obtained an effect that the shortage of capacity in processing bythe disk control unit 30 is dissolved.

On the other hand, in a case where the access request from the hostcomputer A (10) is a read command, the CPU 33 issues an instruction tothe fiber channel controller 31, so as to read out data by accessing tothe logical units 21 and 22 within the disk drive computer 20, intowhich the data blocks required by that access requirement are stored,and it stores the read data through the cache controller 34 into thecache memory 35. After storing the read data into the cache memory 35,the CPU 33 issues instruction to the fiber channel controller 31, so asto transfer the read data stored into the cache memory 35 to the hostdevice A (10), and after the completion of the data transfer, it gives areport of completion in the reading onto the host computer A (10).

Next, explanation will be given on features of the fiber channel network60. The fiber channel network is a long distance and high speedinterface, with which is achieved data transfer at distance of 10 km atthe maximum and at data transfer speed of 100 MB/s at the maximum. Also,the fiber channel has a function of conducting mapping of variousprotocols, such as SCSI, IP, IPI, etc., being located in a higherlogical layer (or higher hierarchy), down to the fiber channel protocolsof a lower logical layer (or lower hierarchy), therefore it is possiblefor the host computer A (10) to perform the data transfer by connectingthe devices having different protocols, such as the SCSI and IP, etc.,to the same fiber channel network. Namely, it has logical compatibilitywith other interfaces.

In the fiber channel, there are defined three connection modes(topologies). First one is a point to point topology, in which the hostdevice is connected to the device one by one. Second one is a FC-ALtopology, in which a plurality of the host computers are connected tothe devices with forming a one loop. The FC-AL connection is establishedby means of a device being called by a FC-AL hub. Third one is a fabrictopology, in which the host computer and the devices are disposed in astar-like connection through the device being called by a Fabric switch.

In the present embodiment shown in FIG. 1, as the fiber channel networkis applied the FC-AL topology, and further therewith the various deviceswhich are connected onto the fiber channel network constitute a computersystem, operating with use of the SCSI mapping protocol. However, suchthe constitution also can be considered that the various devices areconnected with use of the Fabric switches as shown in FIG. 3 so as tooperate in the Fabric topology. Though the fiber channel network formsonly one FC-AL loop in FIG. 1, by forming the fiber channel network witha plurality of FC-AL loops by use of the plural FC-AL hubs, as shown inFIG. 4, and further, by providing the fiber channel network between thehost computer A (10) and the disk control units 30 and 40 beingdifferent from the fiber channel network between the disk control units30 and 40 and the disk drive unit 20 in the loop thereof, there also canbe considered a computer system in which the succession or taking overis necessary both in the fiber channel network between the host computerA (10) and the disk control units 30 and 40 and in the fiber channelnetwork between the disk control units 30 and 40 and in the disk driveunit 20, when succeeding or taking over the logical unit controlinformation.

The transfer of information on the fiber channel is performed by usinginformation of signal level, being called by Order Set, as well asinformation having a fixed format, being called by a frame. Arepresentative one of the Order Set includes SOF (Start Of Frame) foruse in identification of the header of frame (frame header), EOF (StartOf Frame) for use in identification of the end of the frame, IDLE forindicating fact that no frame is transferred on the loop, LIP (LoopInitialization) for use in request of initialization of the FC-AL loop,etc.

Next, explanation will be given on the frame, as a basic unit for thefiber channel to perform the transfer of data. The frame can beclassified broadly into a dataframe and a link control frame on thebasis of functions thereof. The data frame is used for transferringinformation, and also installs the data which is used under the higherrank protocol, such as the SCSI, and command in a pay load portion ofthe data field.

On a while, the link control frame is used, in general, in order toindicate success or failure in the transfer of frames. It includes anACK frame for indicating the receipt of frame, and a frame for noticingthe parameter(s) relating the transfer when performing log-in operation.

Explanation will be given on the format of the frame by referring toFIG. 5. A frame 70 is constructed with the SOF 71, the frame header 72,the data field 73, CRC 74 and EOF 75.

The SOF (Start Of Frame) 71 is an identifier of four (4) bytespositioned at the top of the frame. The EOF (End Of Frame) 75 is anidentifier of four (4) bytes attached at the end of the frame. And, eachborder defined between the frames is indicated by the SOF or the EOF.

The frame header 72 includes a frame type, a higher protocol type, andN_Port addresses of a sender and a receiver (or destination). Each ofthose N_Port addresses indicates an address on the host computers 10 and50 and the disk control units 30 and 40 which are connected to the fiberchannel network.

At the header portion of the data field 73 can be positioned a header ofa higher rank layer, and it is followed by the pay load portion forcarrying the data of themselves. The CRC (Cyclic Redundancy Check) 74 isa check code of four (4) bytes, being provided for the purpose ofchecking the data of the frame header and the data field.

Next, the format of frame is shown in FIG. 6. D_ID (Destination ID) 81is the N_Port address of the receiver side of the frame, while S_ID(Source ID) 82 the N_Port address of the sender side of the frame. Withthe FC-AL topology, the lower eight (8) bits among the twenty-four (24)bits of the N_Port address indicate the address, and in particular, theN_Port address of the FC-AL is called as AL-PA (Arbitrated Loop PhysicalAddress).

Next, explanation will be given on a FCP_CMND (Fiber Channel Protocolfor SCSI Command), a portion of the pay load of the data field 73constructing the frame, and on a FCP_RSP (Fiber Channel Protocol forSCSI Response).

A format of the FCP_CMND is shown in FIG. 7. In FCP_LUN (FCP LogicalUnit Number) field is designated a logical unit which commands by thenumber thereof, while in FCP_CNTL (FCP Control) field is designated acommand control parameter.

In FCP_CDB (FCP Command Descriptor Block) filed 93 is stored a SCSI CDBwhich is for use in transmission of the command at the SCSI interface,while in Operation Code 95 are stored the number(s) indicative of anInquiry or command(s), such as Read, Write, Mode sense, Mode select,etc. Further, there are also stored the LUN, logical block addresses,lengths of transfer blocks, etc., together. In FCP_DL (FCP Data Length)94, there is designated an amount of the data to be transferred with thepresent command by the byte number thereof. With the frame beingconstructed in this manner, the transfer of the SCSI commands isperformed on the fiber channel network.

A format of the FCP_RSP is shown in FIG. 8. The FCP_RSP 100 is used forthe purpose of reporting the result in operation of the SCSI command. InFCP_STATUS 101 are stored SCSI statuses, such as a Good status ofreporting that the command is completed in normal, a Check Conditionstatus of indicating that the command is completed in abnormal, and aBusy status of indicating that the device is in condition that it cannotaccept the command from the host computer, etc.

Next, explanation will be given on roles of commands in the FCP_CMND 90,such as Inquiry, Mode Sense, Mode Select, etc. In FIG. 9 is shownsequence of the Inquiry command. The Inquiry command is used for thehost devices 10 and 50 to search information, such as, the device typeof each one of the devices which are connected to the fiber channelnetwork, the function(s) being supported thereby, the vender name ofproduct, or the product name. Those information are stored into anInquiry data, which is sent to the host computer 10 and 50 by the diskcontrol units 30 and 40 receiving them.

In FIG. 10 is shown a sequence of the Mode Sense command. The Mode Sensecommand is used for the host computers 10 and 50 to refer the parameterof each of the devices being connected to the fiber channel network. Aspages which can be referred by the Mode Sense command, there areincludes a plurality of fixed pages and vender unique pages, and eachpage to be referred can be designated by a Page Code. Those informationare stored in the Mode Sense data, which is sent by the disk controlunit receiving the Mode Sense command.

While, the Mode Select command shown in FIG. 11 is the command for usein changing or altering the parameter(s) which can be referred by theMode Sense command mentioned above. For changing the parameter, it isenough that the page(s) to be changed is designated by the Page Code soas to send a Mode Select parameter list to the disk control unit.

Next, explanation will be given on the control memory 32 which storesthe information being necessary when performing the succession or takingover of the logical unit between the disk control units. The controlmemory 32 is made of the non-volatile memory, therefore the informationstored can be maintained permanently, even if interruption occurs in theelectric power source abruptly.

In the control memory 32, other than the micro-program for controllingthe operations of the disk control units 30 and 40, there are stored aphysical disk drive control table 110 and a logical unit control table120. A format of the physical disk drive control table is shown in FIG.12. In the physical disk drive control table 110, the physical diskdrive number 111 is the number which is assigned to the magnetic diskdrive within the disk drive unit uniquely. A physical disk driveposition 112 stores the logical address indicating that magnetic diskdrive therein. A memory capacity 113 and a number of blocks 114 storetherein the total memory capacity and the total block number of thatmagnetic disk drive, and also a RAID group number 115 stores the numberof the RAID groups to which that magnetic disk belongs. Further, acondition 116 stores therein an information of indicating whether thatmagnetic disk drive is in an on-line condition under which it can beused, or in a blocking condition under which it cannot be used.Furthermore, a kind 117 of memory device is used for identifying thememory device on the fiber channel network 60, i.e., the magnetic diskdevice, the optical disk device, the opt-magnetic disk device, themagnetic tape device or various kinds of library devices.

A format of the logical unit control table is shown in FIG. 13. In thelogical unit control table 120, the logical unit number 121 is thenumber, which is assigned to the logical unit within the disk driveunit, uniquely. A RAID group number is the RAID group number to whichthat logical unit belongs, and a RAID level 123 is the RAID levelthereof. A header address 124 and an end address 125 are the headerlogical block address and the end logical block address, respectively,which are used for the purpose of indicating the position on the RAIDgroup of that logical unit. Information of the physical disk drivecontrol table 110 within the above-mentioned control memory 32 and ofthe logical unit control table 120 can be referred by the Mode Sensecommand which is issued by other device(s), and are changeable in theparameters thereof by the Mode Selection command.

Next, steps will be shown for processing addition of a new disk controlunit 40 to the fiber channel network 60 during the on-line operation andfor succession of the logical unit. This processing steps can be dividedinto operation sequences of the disk control unit 40 and the operationsequences of manager tool installed in the host computer B (50),broadly. In FIG. 14 is shown the operation sequences of the disk controlunit 40, and in FIG. 15 the operation sequences of the management toolinstalled in the host computer B (50), respectively.

First, explanation will be given on the steps of adding the disk controlunit 40 onto the fiber channel network 60 and of setting or deciding theAL-PA. After connecting the FC-AL hub constructing the fiber channelnetwork 60 with the disk control unit 40 to be newly added through afiber channel cable, then the electric power source of the disk controlunit 40 to be newly added is turned ON. Upon turning ON of the electricpower source, the disk control unit 40 executes the processes for linkinitialization, thereby turning it into the condition so that the framescan be transferred on the fiber channel network 60.

Next, the disk control unit 40 which is newly added executes theprocesses for loop initialization. The disk control unit 40, which isnewly added onto the fiber channel network having the FC-AL topologytherein, does not have the AL-PA being effective when the electric powersource is turned ON. Then, the disk control unit 40 being newly addedexecutes the loop initialization processes, thereby being assigned withthe effective AL-PA. The disk control unit 40 to which the AL-PA isdetermined stops the processing once so as to wait for an instructionfrom the management tool which is installed in the host computer B (50).

Next, explanation will be given on the management tool mentioned above.The management tool mentioned above owns a management tooladministration table 130 shown in FIG. 16, in a file form. In theabove-mentioned management tool administration table 130 are stored theinformation of the AL-PA 131 of the disk control unit 30 connected ontothe fiber channel network 60 and the LUN 132 in charge thereof.

The above-mentioned management tool issues one kind of the FPC_CMND 90,i.e., the Inquiry command to all of the devices which are connected ontothe fiber channel network 60, so as to obtain the AL-PA of the diskcontrol unit 40 being newly added. And, it investigates the vender nameof product and the product name thereof, which are stored in theresponse thereto, i.e., in the response to the Inquiry data, and furtherfinds out the device(s) which is not registered on the management tooladministration table 130 by referring to the AL-PA at the frame senderside. Thereby, it is possible to identify the AL-PA of the disk controlunit 40 being newly added, and the AL-PA is newly written into themanagement tool administration table 130.

When once is identified the AL-PA of the disk control unit 40 which isnewly added, the management tool instructs to the disk control unit 40,the logical unit to be conducted the succession thereon, the AL-PA ofthe disk control unit 30 which has been in charge of that logical unit,and the operation mode during the succession of the logical unit of thedisk control unit 30 which has been in charge of that logical unit.

The role(s) of the management tool mentioned in the above can be alsoachieved by using the disk control unit 40 and a panel which isinstalled in the disk control unit 40. In this instance, an operatorinputs the logical unit onto which she/he wishes to succeed or take overthe disk control unit 40 by using a panel 36, so that it finds out thedisk control unit being in charge of that logical unit by using theInquiry command. And, it is enough to memorize the AL-PA of the diskcontrol unit 30 which owns the logical unit to be succeeded. Also, thelogical unit which performs the succession, and the operation modeduring the succession of the logical unit of the disk control unit 30which has been in charge of that logical unit are input by the operator.

Next, the disk control unit 40, in which the logical unit is determinedto perform the succession, enters into processes for succeeding thelogical unit. First of all, the disk control unit 40 issues the one kindof the FCP_CMND, i.e., the Mode Sense command to the disk control unit30, so as to investigate the condition of that logical unit. If thecondition of that logical unit is in normal, the disk control unit 40enters into the processes for succeeding the logical unit, while if thelogical unit is in the blocking condition under which the logical unitcannot be used, this fact is noticed to the operator through the hostcomputer B (50) having the management tool, or through the panel 36.

Next, explanation will be given on a method for setting or establishingthe operation mode during the succession of the logical unit of the diskcontrol unit which has been in charge of that logical unit. This isperformed by issuing the one kind of the FCP-CMND, i.e., the Mode Selectcommand, by means of the disk control unit 40, thereby performingchanges in the settings of the disk control unit 30. Thereafter,responding to the request for process which is issued by the hostcomputer to the disk control unit 30 during the succession of thelogical unit, the disk control unit 30 returns the Busy status in theFCP_REP 100. Here, in case where the Busy status is respondedcontinuously to the request for the command process from the hostcomputer, there is possibility that the request for the command processis in a time-out condition, therefore the process for the succession ofthe logical unit is performed within a time period within a such rangethat it does not fall in the time-out condition.

Next, if there is remained a command (a cueing command) which wasreceived from the host computer but has not yet been processed, then thedisk control unit 30 executes that command to that logical unit, andfurther writes all the Write data to the logical unit which are remainedon that cache memory into the disk drive unit 20. Thereby, even in acase where the device in charge of the logical unit is shifted from thedisk control unit 30 to the disk control unit 40, the data within thedisk drive unit 20 is guaranteed, in particular in the compatibilitythereof.

Next, the disk control unit 40 makes copy of the contents of the controlmemory 32, in which are stored the physical drive control table 110 andthe logical unit control table 120, being necessary when succeeding thatlogical unit from the disk control unit 30 to the disk control unit 40.The copy of the control memory 32 is realized by operations that thedisk control unit 40 issues the one kind of the FCP_OMND 90, i.e., theMode Sense command to the disk control unit 30, and that the informationof the control memory 32 of the disk control unit 30 is read out so thatthe contents thereof is written into the control memory 32 of the diskcontrol unit 40.

When receiving the information of the physical disk drive control table11 and the logical unit control table 120 which are necessary for thesuccession of the logical unit, the disk control unit 40 executesinternal processes to be in a condition of enabling the commandprocesses, thereby preparing for the request of the command processes.From the host computer 10 the processes can be performed withcontinuity, by changing the route of access of the logical unit from thedisk control unit 30 which has been existing before to the disk controlunit 40 which is newly added to.

Further, as a method for succeeding the control information of thelogical unit between the above-mentioned disk control units 30 and 40,the disk control unit existing on the fiber channel network succeeds ortakes over the control information by a unit of the logical unit fromother disk control unit which is connected to the same fiber channelnetwork during the on-line operation of the computer system, andthereafter it is in charge of the request for command processes issuedto that logical unit from the host computer. This is applicable to loaddistribution between or among the disk control units existing on thefiber channel network, and also to a means for unifying severalprocesses which are performed by the plurality of the disk control unitsinto an arbitrary disk control unit.

Next, explanation will be given on a method, in which no change isnecessitated in the access route from the host computer by the operator,when the charge of the logical unit is shifted from the disk controlunit 30 to the disk control unit 40. As is shown in FIG. 17, the diskcontrol unit installs the fiber channel adapters of the same number tothe logical units which were in charge, and in each of them isestablished the AL-PA. The AL-PA in each is administrated as a pairtogether with the logical unit being in charge of. When the charge ofthe logical unit is shifted from the disk control unit 30 to the diskcontrol unit 40, not only the control information of the logical unit,but also the AL-PA is succeeded. Thereby, since it is not acknowledgedfrom the host computer that the charge of the logical unit is shiftedfrom the disk control unit 30 to the disk control unit 40, it ispossible to issue the request of processes in the same manner as beforein the succession of that logical unit, thereby rendering the change inthe access route unnecessary.

In this manner, with application of the present invention, it ispossible to perform the load distribution between or among the diskcontrol units by adding the disk control unit 40 to the fiber channelnetwork 60 during the on-line operation. Further, in accordance with thesame method, it is also possible to change the logical units of whichthe plural disk control units on the fiber channel network are incharge, freely, thereby achieving the load distribution and integrationbetween or among the existing disk control units.

As is fully explained in the above, according to the present invention,in the fiber channel network having the existing disk control unit(s)which is connected thereto, it is possible to achieve the loaddistribution and the integration of processes between or among the diskcontrol units, by adding a new memory controller(s) thereto during theon-line operation so as to succeed the charge of processes of thelogical unit(s) thereof, thereby obtaining an increase of the processingcapacity of the data storage system as a whole.

In more details, when the existing disk control unit(s) which isconnected to the fiber channel network being standardized by the ANSIX3T11 falls into a condition of shortage in processing capacity thereof,a new disk control unit(s) can be added to the computer system duringthe on-line operation thereof, thereby obtaining the load distribution.

Further, according to the present invention, at the maximum, 127 sets ofthe devices can be connected with the FC-AL (Fiber Channel ArbitratedLoop) topology, and bout 1,700 sets of the devices with the Fabrictopology, and by applying as an interface a fiber channel which has afeature that it can be logged-in into the fiber channel networkautomatically by connecting the device(s) physically to the fiberchannel network during the on-line operation, so as to issue the linkreset from the device side, it is possible to add, not only two sets ofthe disk control units, but also the plurality sets of the disk controlunits therein, during the on-line operation, thereby enabling expansionof the data storage system with flexibility, without troubling by theinitial settings thereof.

What is claimed are:
 1. A method for a data storage system, having oneor more of memory device(s), a host device, and a memory controller forcontrolling transfer of data stored in said memory device(s) respondingto an instruction from said host device, the memory controller beingconnected to an interface for use in connection with said host device ina route which stands between said memory device(s) and said host devicelogically and connects to said host device logically, comprising: addinga new memory controller into said data storage system during on-lineoperation thereof in addition to said memory controller which isprovided previously; turning on an electric power source of said newmemory controller; and identifying said new memory controller by eitherone of a tool being operative on said host device and said memorycontroller, thereby sharing processing capability with said previouslyprovided memory controller and said newly added memory controller.
 2. Amethod for treating a data storage system as described in the claim 1,wherein there comprises a step for executing an initialization processof said route in place of the step of turning on said electric powersource of said new memory controller.
 3. A method for treating a datastorage system as described in the claim 1, wherein said memorycontroller has a function of storing control information of a logicalunit of said memory device(s), and further comprising a step of startingstorage of the control information of said logical unit.
 4. A method fortreating a data storage system as described in the claim 1, wherein saidmemory device(s) comprises at least one from a magnetic disk device, anoptical disk device, an opt-magnetic disk device, a magnetic tape deviceand a library device.
 5. A method for a data storage system, having oneor more of memory device(s), a host device, and a memory controller forcontrolling transfer of data stored in said memory device(s) respondingto an instruction from said host device, the memory controller beingconnected to an interface for use in connection with said host device ina route which has been standing in advance between said memory device(s)and said host device logically and connects to said host device and saidmemory controller logically, comprising: adding a new memory controllerinto said data storage system during on-line operation thereof;executing an initialization process of said route; and obtaininginformation for said host computer to identify the memory controllerhaving been standing in advance, uniquely, by said new memorycontroller, the new memory controller, thereby sharing processingcapability with said memory controller having been standing in advance.6. A method for treating a data storage system as described in the claim5, wherein said memory controller has a function of storing controlinformation of a logical unit of said memory device(s), and furthercomprising a step of starting storage of the control information of saidlogical unit.
 7. A method for treating a data storage system asdescribed in the claim 5, wherein said memory device comprises at leastone from a magnetic disk device, an optical disk device, an opt-magneticdisk device, a magnetic tape device and a library device.
 8. A memorycontroller, the memory controller being connectable to a data storagesystem during an on-line operation, the data storage system including ahost device, a storage means including one or more memory device, and asecond memory controller, the memory controller capable of being addedinto logically standing between said host device and said storage meansand comprising: connection means connectable to an interface used forconnection with said host device in a route being logically connected tosaid host device; an internal memory for storing control information ofa logical unit of said memory device(s) which is stored in said secondmemory controller already standing between said host device and saidstorage means; and means for controlling transfer of data stored in saidmemory device(s) depending upon an instruction from said host device,wherein the memory controller is identified by either one of a toolbeing operative on said host device and said second memory controller,the memory controller thereby sharing processing capability with saidsecond memory controller.
 9. The memory controller according to claim 8,wherein said memory controller is connected to said interface used forconnection with said one or more memory device in said route logicallyconnecting between said memory device(s) and to said second memorycontroller.
 10. The memory controller according to claim 8, wherein saidroute is a fiber channel which is standardized by ANSI X3T11.
 11. Thememory controller according to claim 8, wherein said internal memoryholds information for use in controlling the logical unit of said one ormore memory device until said internal memory is reset.
 12. The memorycontroller according to claim 8, wherein said one or more memory devicecomprises at least one of a magnetic disc device, an optical discdevice, an opto-magnetic disc device, a magnetic tape device, and alibrary device.